Field of the Invention
The present invention relates to a sheet handling apparatus.
Description of the Related Art
Examples of sheet handling apparatus include stackers, sorters, staplers, binders, folders and the like, that are typically arranged in a print production line so as to receive a sequence of media sheets that have been printed in a printer or copier. Frequently it is desired that the sheets, before they are processed further, are aligned correctly in the direction Z in the plane of the transport path and normal to the transport direction X. For example, a lateral edge of the sheets should be oriented in parallel with the transport direction X, and preferably the position of this edge in the direction Z should be identical for all sheets. In a practical reproduction line, however, this requirement is not always fulfilled when the sheets arrive at the handling apparatus. The sheets may be offset relative to one another in the direction Z and/or may be skewed, i.e. rotated in the X-Z plane.
The sheet alignment mechanism is provided for correcting at least one of these alignment errors or preferably both of them (a so-called SZ-correction).
When the sheets to be handled have all the same length, the distance between the last pinch and drive mechanism and the sheet alignment mechanism may be selected such that the pinch and drive mechanism releases the trailing edge of the sheet when a leading part of the sheet is gripped by the alignment mechanism and the sheet starts to be rotated or moved in the lateral direction Z.
However, when sheets of varying length are to be processed, a situation may occur that a relatively long sheet is supplied and the trailing part of the sheet is still pinched by the last pinch and drive mechanism while the alignment mechanism already attempts to shift or rotate the sheet. In such a case, in order to avoid that the alignment process is compromised or the sheet is damaged, the pinch and drive mechanism is lifted in order to release the sheet under the control of the controller.
U.S. Pat. No. 6,817,609 B2 discloses the sheet handling apparatus of the type indicated above, which has a plurality of liftable pinch and drive mechanisms and is capable of handling a relatively broad bandwidth of sheets with varying lengths and also sheets with varying widths. As is pointed out in this document, when even longer sheets are to be processed, it is necessary to add further liftable pinch and drive mechanisms (and to increase the length of the transport path accordingly), which means that a relatively costly modification of the apparatus is required.